Structure and mechanical properties of hot rolled sheets of Al – 2% Cu – 2% Mn – 0.4% Si – 0.2% Zr alloy subjected to friction stir welding

On the example of a hot-rolled sheet of aluminum alloy Al – 2Cu – 2Mn – 0.4Si – 0.2Zr% (wt.), the possibility of obtaining joints providing high mechanical properties and thermal stability by friction stir welding (FSW) is considered. From a non-homogenized ingot with a thickness of 40 mm from this alloy a sheet with a thickness of 4 mm was obtained on a laboratory rolling mill at a temperature of 350 оC (reduction degree 90 %). After rolling, cards were cut out of the sheet, which were joined by the double-sided STP method in two modes. For mode 1, the pressing force of the tool was 7551.12 N at a speed of longitudinal movement of the tool of 0.3 m/min, and for mode 2 — 7256.92 N and 0.125 m/min. The tool rotation frequency for the two modes was the same — 800 rpm. The structure and properties of the joints were studied before and after annealing at a temperature of 400 оC for 3 hours. It was found that the experimental alloy has high thermal stability, due to which, after FSW in the weld and heat-affected zones, the decrease in hardness does not exceed 10 % and remains practically unchanged. after annealing. It is shown that the FSW method makes it possible to obtain a high quality of welded joints, retaining almost the original strength (σw = 280–290 MPa) with a significant increase in relative elongation (δ from 3 to 12–16%). The increase in plasticity is due to the formation of an ultrafine-grained structure in the weld zone (grain size less than 5 μm), which can be explained by the occurrence of dynamic recrystallization during the FSW. The totality of the results obtained allows to consider the use of the FSW method to be promising for obtaining equal-strength and thermally stable joints of rolled sheets of experimental alloys of the Al – Cu – Mn (Si, Zr) system, the structure of which differs from the grade alloys of the 2xxx series by a higher content of Mn-containing dispersoids. This work was supported by the Russian Science Foundation grant No. 20-19-00249.